Ok I have read a few posts and this makes me wonder if I'm missing something about bike brakes. Why would bike brakes need to be bled periodically? If the hydraulic system is closed and not in a vacuum then contaminants (dirt, air and moisture) should not get into the fluid. Reminds me of the Jiffy Lube type shops that recommend changing car brake fluid because it's old. Some of the posts suggest to drain and allow the lines to "air out" after cleaning. Depending on atmospheric conditions the ambient air can contain high amounts of moisture which can contaminate the lines. Using a dry inert gas like nitrogen would be better. Anyways just wondering what I don't know.
I've always wondered the same thing. I go 3-4 years on a set of brakes and never have to bleed and never notice a loss of performance.
also, you degrade the fluid's performance with heat.. if you boil the fluid when you get the brakes cooking..... No such thing as a perfect seal either.... bet your fluid isnt anything close to the same color as it was when it was fresh
they need to be bled periodically due to the repeated heating and cooling cycles brake fluid undergoes as part of its normal life. as time passes the fluid begins to degrade and stopping becomes more difficult. granted, if you dont use the brakes much, then the time it takes for the fluid to break down will be longer. oh and dont air out the lines, thats just dumb. if you have a problem with your lines, get new braided stainless lines! they are sexy!!! bottom line: bleed your brakes. and bleed them correctly! an incorrect bleed is worse than no bleed at all
Mk3 you make all good points but the answer is to remove air. Wish we lived in a perfect world but the reality is it's pretty hard to get 100% of the air out of the brake fluid to start with. You don't need to bleed them that often. It kills me to see guys posting here they are paying $60 plus to have their LBS do the bleed. It's really simple to do.
Bleed your brakes and you will find out the reason. Added to the reasons above, the seals break down and the fluid turns black. Two, you don't notice them loosing power because it happens slowly. With the right fittings and syringe it is very easy to do. Dean
That's okay. I don't have clear lines. Seriously though I check things regularly and as long as the pistons are moving freely I will leave them alone. After reading more posts I feel the need to bleed my brakes.
The fluid goes bad once it gets overheated. Contaminents get in the fluids and or moisture gets in over time. After 3 years, the boiling point of the fluid will have dropped severely because of junk getting in the lines. Once athe fluid reaches boiling point, the fluid has broken down and you need to get it out asap. Plenty of reasons to change fluid... and really it is a simple job that will keep the brakes working well. You don't want a soft pedal when it counts right (aka sudden brake failure due to overheated fluid)? Btw, you don't ever want to drain all the fluid out (in a car), ever. Air will get into the master, the lines, or circuits and moisture will develop and once its in there its almost impossible to get out. There's a lot of do's and don'ts and I'm sure I missed a whole slew, but oh well.
I agree with trying not to clear the lines, causes some headaches later. Bleed until there are NO bubbles, then bleed more. Brake fluid is cheap, run a shit pile of fluid through the system. Also... brake fluid sucks up moisture... make sure your CAN of fluid is sealed very well. Shelf life isnt that long once opened from what i've read....
Are we gonna talk about DOT 3-4 systems vs. Mineral oil too? Bleed 'em once a year. Hell, Change the pads and scuff the rotors while your at it. Brakes are something that really should "maintained" even if they don't "need" it.
Shelf life is 6weeks max after opened, Glycol will readily absorb ambient moisture, and unless you live in Vegas their is moisture everywhere.
Ask anyone with motor racing experience - open a bottle, use it, and discard the rest. And make sure to properly dispose the excess brake fluid, don't just dump it in the drain
I can understand the idea of chemical breakdown due to heat, but what temperature does the brake fluid boil or start to break down? I think my Juicy's have DOT4. I don't buy the idea of air and contaminants "getting in" the system. If there are leaks then the oil would leak out since the brake system is under positive pressure when braking and not lower than same as atmosphere when not braking, but never in a vacuum where air can get sucked in.
Not sure if contaminates get in or not but there is wear going on in the inside. As I said before you can see the contaminates when you flush the system. But it seems like you have already made up your mind so I suggest that you not do any brake maintenance. Dean
you are equating the size of an air molecule and the size of a brake fluid molecule. Seals also wear out, expand with heat etc. Lots of heat cycles between dissimilar materials can create imperfect sealing. Why do we change fluid in our forks? Surely no dirt gets past those seals! And thats not even a high heat application. Why do we change the oil in our cars? The rings on the piston surely seal 100%!
Car oil burns due to the high heat of combustion. Piston rings do not seal good at all, that's why compressors use a wiper ring. It's not that my mind is made up, I never thought much about having to change fluid in my fork either... damn you guys and your bike gear smartness! Well I guess I'll go for it and change the brake fluid and see what I find. I guess I'm a little curious now anyways.
About 600F, give or take 25 degrees depending on brand. If you don't buy the idea of contaminants and moisture getting in, open up your brakes and drain them. If it's been over a year, they will be black. No sense arguing with you over the internet. Prove to yourself so that you will never doubt that the Internetz is always right.
Now that you brought the subject up! Nothing makes a fork work better than a oil change...do it the results my surprise ya. I always change the oil in new forks after about 10-20 hours of use. Dean
